1. Field of the Invention
The present invention relates to a novel process for the preparation of aryl hydrazines of the following formula: ##STR1## and indazoles of the following formula: ##STR2## as described further below. Aryl hydrazines and indazoles are useful pharmacological intermediates.
2. Description of the Prior Art
Aryl hydrazines are useful as intermediates for dyes, agricultural chemicals and pharmaceuticals. Indazoles are useful as pharmaceuticals, dyes and photographic coupling agents.
Currently known methods for preparing aryl hydrazines involve reducing the corresponding diazonium salts with sulfite or other reducing agents (Coleman, G., Org. Syn. Coll. Vol. I, 442 (1941)), or by electrolysis (Takayanagi, J. Chem. Soc. Japan 53, 427 (1932)). The former method is not generally applicable to substituted hydrazines, and requires careful attention to reaction conditions. The latter method requires specialized apparatus. Other methods involve N-animation of anilines, which require specialized reagents (Ohme, R. et al., in Preparative Organic Chemistry, Hilgetag et al., Eds., John Wiley & Sons, New York, p. 586 (1972)), and rearrangements of N-halo ureas (Murakami, Y., Chem. Pharm. Bull. 31, 423 (1983)). All of these methods require that the corresponding aniline be available.
The prior art reveals that Grignard reagents have been added to the N.dbd.N double bonds of diazirenes (Angewandte Chemie 73, 220 (1961)) and diazoalkanes (J. Org. Chem. 23, 1595 (1958)). Additionally, tert-butyl magnesium chloride has been added to di-t-butylazodicarboxylate, and the product converted to t-butylhydrazine (J. Org. Chem. 26, 4336 (1961)). The addition of enolates to azodicarboxylates has also been reported by J. C. Vederas at the International Symposium on the Chemistry of Natural Products, Edmonton, Alberta, Canada, June 25, 1985.